conlang: Unify binding operations!

This breaks out the pattern matching/unification algorithm from cl-interpret/interpret.rs to cl-interpret/pattern.rs

TODO: pattern destructuring in const, static :^)

compiler/cl-interpret/src/pattern.rs

@@ -0,0 +1,130 @@
+//! Unification algorithm for cl-ast patterns and ConValues
+//!
+//! [`variables()`] returns a flat list of symbols that are bound by a given pattern
+//! [`substitution()`] unifies a ConValue with a pattern, and produces a list of bound names
+
+use crate::{
+    convalue::ConValue,
+    error::{Error, IResult},
+};
+use cl_ast::{Literal, Pattern, Sym};
+use std::{collections::HashMap, rc::Rc};
+
+/// Gets the path variables in the given Pattern
+pub fn variables(pat: &Pattern) -> Vec<&Sym> {
+    fn patvars<'p>(set: &mut Vec<&'p Sym>, pat: &'p Pattern) {
+        match pat {
+            Pattern::Name(name) if &**name == "_" => {}
+            Pattern::Name(name) => set.push(name),
+            Pattern::Literal(_) => {}
+            Pattern::Ref(_, pattern) => patvars(set, pattern),
+            Pattern::Tuple(patterns) | Pattern::Array(patterns) => {
+                patterns.iter().for_each(|pat| patvars(set, pat))
+            }
+            Pattern::Struct(_path, items) => {
+                items.iter().for_each(|(name, pat)| match pat {
+                    Some(pat) => patvars(set, pat),
+                    None => set.push(name),
+                });
+            }
+            Pattern::TupleStruct(_path, items) => {
+                items.iter().for_each(|pat| patvars(set, pat));
+            }
+        }
+    }
+    let mut set = Vec::new();
+    patvars(&mut set, pat);
+    set
+}
+
+/// Appends a substitution to the provided table
+pub fn append_sub<'pat>(
+    sub: &mut HashMap<&'pat Sym, ConValue>,
+    pat: &'pat Pattern,
+    value: ConValue,
+) -> IResult<()> {
+    match (pat, value) {
+        (Pattern::Array(patterns), ConValue::Array(values))
+        | (Pattern::Tuple(patterns), ConValue::Tuple(values)) => {
+            if patterns.len() != values.len() {
+                Err(Error::ArgNumber { want: patterns.len(), got: values.len() })?
+            }
+            for (pat, value) in patterns.iter().zip(Vec::from(values).into_iter()) {
+                append_sub(sub, pat, value)?;
+            }
+            Ok(())
+        }
+        (Pattern::Tuple(patterns), ConValue::Empty) if patterns.is_empty() => Ok(()),
+
+        (Pattern::Literal(Literal::Bool(a)), ConValue::Bool(b)) => {
+            (*a == b).then_some(()).ok_or(Error::NotAssignable)
+        }
+        (Pattern::Literal(Literal::Char(a)), ConValue::Char(b)) => {
+            (*a == b).then_some(()).ok_or(Error::NotAssignable)
+        }
+        (Pattern::Literal(Literal::Float(a)), ConValue::Float(b)) => (f64::from_bits(*a) == b)
+            .then_some(())
+            .ok_or(Error::NotAssignable),
+        (Pattern::Literal(Literal::Int(a)), ConValue::Int(b)) => {
+            (b == *a as _).then_some(()).ok_or(Error::NotAssignable)
+        }
+        (Pattern::Literal(Literal::String(a)), ConValue::String(b)) => {
+            (*a == *b).then_some(()).ok_or(Error::NotAssignable)
+        }
+        (Pattern::Literal(_), _) => Err(Error::NotAssignable),
+
+        (Pattern::Name(name), _) if "_".eq(&**name) => Ok(()),
+        (Pattern::Name(name), value) => {
+            sub.insert(name, value);
+            Ok(())
+        }
+
+        (Pattern::Ref(_, pat), ConValue::Ref(r)) => append_sub(sub, pat, Rc::unwrap_or_clone(r)),
+
+        (Pattern::Struct(path, patterns), ConValue::Struct(parts)) => {
+            let (name, mut values) = *parts;
+            if !path.ends_with(&name) {
+                Err(Error::TypeError)?
+            }
+            if patterns.len() != values.len() {
+                return Err(Error::ArgNumber { want: patterns.len(), got: values.len() });
+            }
+            for (name, pat) in patterns {
+                let value = values.remove(name).ok_or(Error::TypeError)?;
+                match pat {
+                    Some(pat) => append_sub(sub, pat, value)?,
+                    None => {
+                        sub.insert(name, value);
+                    }
+                }
+            }
+            Ok(())
+        }
+
+        (Pattern::TupleStruct(path, patterns), ConValue::TupleStruct(parts)) => {
+            let (name, values) = *parts;
+            if !path.ends_with(&name) {
+                Err(Error::TypeError)?
+            }
+            if patterns.len() != values.len() {
+                Err(Error::ArgNumber { want: patterns.len(), got: values.len() })?
+            }
+            for (pat, value) in patterns.iter().zip(Vec::from(values).into_iter()) {
+                append_sub(sub, pat, value)?;
+            }
+            Ok(())
+        }
+
+        (pat, value) => {
+            eprintln!("Could not match pattern `{pat}` with value `{value}`!");
+            Err(Error::NotAssignable)
+        }
+    }
+}
+
+/// Constructs a substitution from a pattern and a value
+pub fn substitution(pat: &Pattern, value: ConValue) -> IResult<HashMap<&Sym, ConValue>> {
+    let mut sub = HashMap::new();
+    append_sub(&mut sub, pat, value)?;
+    Ok(sub)
+}